The present invention relates to an electronic visual display test apparatus, and more particularly it relates to a test instrument providing a visual display wherein two display elements move countercurrent with each other when the frequency of the crystal undergoing test lies within a predetermined acceptable frequency range.
Certain crystalline materials when subjected to the influence of an electrical field, tend to vibrate at a periodic rate, commonly known as the resonant frequency. These vibrations have long been used in crystal oscillator circuits to control the frequency of the oscillator, because the crystal presents a very low impedance feedback path to the oscillator at precisely its resonant frequency. The instrinsic resonant frequence of a crystal typically varies from crystal to crystal because of a number of factors which cannot be completely controlled such as physical size and temperature. However, the resonant frequency of any crystal can be made to vary slightly by the addition and substraction of capacitance or inductance. Consequently, precision electronic apparatus using time base crystal oscillators provide a small trimmer capacitor or inductor to enable tuning of a crystal to a precise desired frequency. Incident to the production in quantity of such instruments, such as digital electronic timepieces, it has been necessary to ascertain whether the crystals to be included in such timepieces have frequencies lying within the range of adjustment provided by the timepieces. The present invention provides a visual display set that makes possible a rapid determination of whether incoming crystals operate at frequencies lying within the predetermined range.
Heretofore, determination of the range of a quartz crystal has been accomplished primarily with test oscillator circuits and complex peripheral apparatus such as precision digital frequency counters capable of displaying the actual crystal frequency. Operators have viewed such counters and then mentally determined whether the indicated crystal frequency was within or beyond the acceptable frequency range. The use of those frequency counters, especially in production line situations, resulted in eye strain and undue operator fatigue. Errors in accepting crystals with frequencies out of range resulted in subsequent difficulties with equipment including those erroneously accepted crystals. In addition, each digital frequency counter tended to be very expensive because of the substantial costs of the precision master oscillators which were required and contained in each such counter. In addition, reading the required digits of such counter caused the operator to spend a substantial amount of time with each crystal undergoing range check. Thus, incoming crystal acceptance rates were slow because of delays at the test station, a drawback only overcome by increasing the number of such stations. These and other disadvantages are overcome by the present invention.
In view of the foregoing, it is an object of the present invention to provide a simple visual indicator enabling rapid and unmistakable determination that an incoming crystal oscillates at a frequency lying within a predetermined range.
Another object of the present invention is to provide an incoming crystal inspection unit wherein display elements representing each limit of the acceptable frequency range move countercurrent to one another when the incoming crystal undergoing tests lies within the range.
A further object of the present invention is to provide an incoming crystal inspection unit which is highly portable and self-contained that may be manufactured at a cost far less than such units heretofore available.